This application claims the priority benefit of Taiwan application serial no. 91100094, filed on Jan. 7, 2002.
1. Field of the Invention
This invention relates in general to a chip structure with bumps and a process for fabricating the chip, and more specifically relates to bumps made of specific material so that the bumping process is simplified and the manufacturing cost is reduced.
2. Description of Related Art
Recently, following the high-development of information technology, electronic products are commonly used in the public. The design fashions of various electronic products trends also generally towards lightness, thinness, shortness and smallness. Therefore, as far as the field of semiconductor packages is concerned, a lot of package structures are provided in high density type. In some fields of package, bumps are formed on a chip to perform Flip Chip Packaging or Tape Carrier Packaging. Bumps are generally divided into 2 types, one is made of solder, the other is made of gold. The bumps made of gold in prior art will be described as follows.
FIG. 1 to FIG. 5 are schematic cross-sectional views showing the progression of steps for producing a bump made of gold in accordance with a conventional method.
As shown in FIG. 1, a chip 110 which has an active surface 112 and bonding pads 116 (only one bonding pad is shown) is provided. The bonding pads 116 are formed on the active surface. A passivation layer 114 is formed on the active surface 112 and a1a1 exposes the bonding pads 116 so that the chip 110 is electrically connected to other outside circuit (not shown) through the bonding pads 116. The Under Bump Metal process is followed to form a barrier layer 120 on the active surface 112 of the chip 110 by sputtering method. The barrier layer 120 covers bonding pads 116 and the passivation layer 114. The material of the barrier layer 120 is for example TiW etc., wherein a thickness of the barrier is about thousands of angstrom. Then a seed layer 130 is formed on the barrier layer 120 by electrical plating or sputtering method. After that, the Under Bump Metal 140 is completed. The material of seed layer 130 is for example gold, wherein a thickness of the seed layer is about 1000 angstrom, and the Under Bump Metal 140 is composed of the barrier layer 120 and seed layer 130.
As shown in FIG. 2, a photolithography process is performed. A photo resist layer 150 is formed on the seed layer 130. After the photo resist layer 150 has been exposed and developed, a pattern (not shown) is transferred to the photo resist layer 150 so that openings 152 (only one opening is shown) which exposes bonding pads 116 are formed in the photo resist layer 150.
As shown in FIG. 3, a bumping process follows. Bumps 160 (only one bump is shown) are filled in the openings 152 of the photo resist layer 150, wherein the material of the bump 160 is gold.
Referring to FIG. 3 and FIG. 4, the photo resist layer 150 is removed from the surface of the seed layer 130.
Referring to FIG. 4 and FIG. 5, the Under Bump Metal 140 which is exposed is removed by an etching method. Then an annealing process is performed so that the metal ions with defects which are in the bumps 160 are rearranged to be in a stable state.
As it is described above, the bumping process is complicated, high cost and is not so effective a manufacturing process.
According to the foregoing description, an object of this invention is to provide a structure and a fabricating process of a bump so that the bumping process is simplified and cost down by changing the material of the bumps.
To attain the foregoing and other aspects, the present invention proposes a chip structure with bumps comprising: a chip and at least a bump. Wherein the chip has an active surface and at least a bonding pad, and the bonding pad is formed on the active surface. The bump is disposed on the bonding pad, and the bump comprises a medium layer, a bump body and a bump body passivation layer. The medium layer is disposed on the bonding pad, and a material of the medium layer includes zinc. A bump body is disposed on the medium layer, and a material of the bump body includes nickel. A bump body passivation layer covers the bump body except for a portion of the bump body that connects to the medium layer, wherein a material of the bump body passivation layer includes gold.
Also to attain the foregoing and other aspects, the present invention proposes a process for fabricating a chip with bumps comprising the following steps. First providing a chip that has an active surface and at least a bonding pad, wherein the bonding pad exposes the active surface. Then performing an activation step, depositing a medium layer on the bonding pad. Forming at least a bump body on the medium layer in an electroless plating way, and forming a bump body passivation layer covering the bump body except for a portion of the bump body that connects to the medium layer.
According to a preferred embodiment of the present invention, the material of the bump body is nickel, and the material of the bump body passivation layer is gold. The height of the bump body is about 5 to 10 microns, and the height of the bump body passivation layer is about 1 to 3 microns. The bump body and the bump body passivation layer are formed by electroless plating.
As it is described above, the feature of the present invention is to change the material of the bumps so that the bumps can be formed on the bonding pads of a chip in a simplified manufacturing process.